In the extratropical latitudes (where, for example, Columbia University is located) we have a fairly good understanding of the basic dynamical processes that control the atmosphere's behavior. This understanding has two manifestations. With sophisticated numerical models, we can predict the extratropical weather fairly well, up to a week ahead or so. We also have much simpler mathematical models which, though not accurate enough to produce good weather forecasts, capture the basic dynamics of the atmosphere and can at least qualitatively simulate the important phenomena such as winter storms, fronts, waves in the jet stream, etc. These simpler models are derived as approximations to the full equations of atmospheric motion and energy. They form the core of our understanding and guide us as we analyze both observations and numerical simulations of the extratropical atmosphere.

The atmosphere behaves differently in the tropics than in the extratropics, and is less well understood. Weather forecasts are considerably less accurate in the tropics, and many of the largest uncertainties in our simulations of the global climate are related to gaps in our understanding of tropical atmospheric processes. In particular, we do not understand, in a wide range of circumstances, what controls where and when rain falls in the tropics. This lack of understanding and predictive capability is expressed by our lack of simple mathematical models for the tropics that combine economy and correctness as successfully as the simple extratropical models do.

My research efforts are focused on improving our understanding of tropical dynamics. I focus to a large extent on what controls rainfall patterns and their variability on time scales of days to decades. My associates and I use mathematical models of varying degrees of complexity for this purpose. Some can be solved with pencil and paper, and some (more typically) require powerful computers. We also analyze observational data, which is important to keep a theoretical and modeling research program grounded in reality.